Originally Posted by
Lansow
There's your problem. No, I'm not trolling. My guild was trying with a very similar setup to yours(we had a shaman instead of a retadin and two pallies + resto druid instead of a priest). We got very close on many attempts, but the add tank was experiencing the exact same issue as you(namely healer aggro). It's directly related to bears having a hard time generating snap threat when more than 5 adds are within 10 yards of each other.
Our solution was to sit one of the bear tanks and swap in a pally tank. Both times we've done this we downed the boss within 2 pulls.
YMMV, but add tanking on this fight is far more difficult for druids than warrior/dk/pally.